High-pressure electric discharge lamp having magnetically actuable arc ignition means,and apparatus for starting such a lamp



June 24, 1969 HIGH-PRESSURE ELECTRIC D'IS N C. BEESE CHARGE LAMP HAVING MAGNETICALLY ACTUABLE .ARC IGNITION MEANS AND APPARATUS Filed. Dec. 6, 1966 FIGI FOR STARTING SUCH A LAMP III Norman C. Beese AGEN lune 24, 1969 HIGIFPRESSURE ELECTRI ACTUABLE ARC N. c. BEESE 3,452,236 C DISCHARGE LAMP HAVIN A TICALLY IGNITION MEANS AND APP A S FOR STARTING SUCH A LAMP Filed Dec. 6, 1966 44 Fl G. 5.

sheet Z ors June 24, 1969 N Q BEESE 3,452,236

HIGH-PRESSURE ELECTRIC DISCHARGE LAMP HAVING MAGNETIGALLY ACTUABLE ARC IGNITION MEANS, AND APPARATUS FOR STARTING SUCH A LAMP 3 Sheetv Filed Dec. 6. 1966 o 0 6 Mw 3 S 4 0 3 5 4|' z l l |H 7/ L A o u o I 2 O 2 4 LMU 8 0 3 3 0 4. 0 T VT 7. G F

United States Patent O 3,452,236 HIGH-PRESSURE ELECTRIC DISCHARGE LAMP HAVING MAGNETICALLY ACTUABLE ARC IGNITION MEANS, AND APPARATUS FOR STARTING SUCH A LAMP Norman C. Beese, Verona, NJ., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 6, 1966, Ser. No. 599,532 Int. Cl. H013' 1/50, 1/52, 21/22 U.S. Cl. 313-152 18 Claims ABSTRACT F THE DISCLOSURE arc from one electrode that is transferred to the other electrode to effect lamp ignition.

Background of the invention This invention relates to electric discharge devices and has particular reference to a high-pressure short-arc lamp and an improved apparatus for starting such lamps. As is well known, high-pressure gaseous discharge lamps require a much higher starting voltage than operating voltage. In the case of short-arc lamps, starting is generally accomplished by applying a series of high-voltage pulses in the order of 20 to 50 kilovolts to the lamp electrodes to ionize the gas and strike the arc. A starting circuit of this type `wherein the high-voltage pulses are produced by a spark-gap oscillating circuit is described in U.S. Patent No. 2,708,251 issued to C. M. Rively. Such pulse-type starting circuits are expensive, bulky, and critical in that they must be properly adjusted to avoid excessive power inputs which could destroy the fragile lead-in conductors or otherwise damage the lamp.

Discharge lamps and starting circuits utilizing magnetically-actuated auxiliary electrodes are also known. Lamps and circuits of this type are described in U.S. Patent Nos. 1,086,105 and 1,144,396. However, the prior art structures are inherently unsuited for use in high-intensity discharged amps insofar as the auxiliary electrode remains in the discharge path and requires a large or constantly energized electromagnet.

Summary of the invention It is accordingly the general object of the present invention to provide an improved high-pressure electric discharge lamp which has a long useful life and can be reliably started with voltages of much lower magnitude than those heretofore required for lamps of this type.

Another object is the provision of an improved shortarc lamp that is practical from a manufacturing standpoint and can be repeatedly and reliably started without the use of high-voltage auxiliary equipment or impairing its performance.

Still another object is the provision of a compact and inexpensive apparatus which will quickly and reliably start such lamps on conventional power supplies without interfering with or impairing the normal operation of the lamp.

Brieiiy, the aforesaid objectives and other advantages are achieved in accordance with the present invention by mounting a exible arc initiating assembly of conjoined refractory metal strips within the lamp in such a way that the medial portion of the assembly is free to swing in pendulum-like fashion toward and away from the electrodes.

According to a preferred embodiment, one end of the starter assembly is hingedly attached to the anode of a short-arc lamp and the opposite end of the assembly is hingedly attached to but insulated from the cathode so that a metal striker bar carried by the assembly will lmake and break contact with a predetermined portion of the cathode. The lateral movement of the assembly and striker bar is achieved by means of an armature of magnetizable material that is fastened to the assembly and is actuated by an electromagnet located outside the lamp. The spacing between the striker bar and cathode and the other parameters are such that when the normal operating voltage is applied to the lamp electrodes and the striker bar is actuated and then returned to its normal break-contact position, it draws an arc of sufficient length from the cathode that the arc is transferred to the anode by convection currents generated by the heated filled gas--thus starting the lamp.

The invention includes novel arrangements for swingably attaching the arc-initiating structure to the electrodes and making them integral parts of a subassembly that can be inserted into the envelope through one of its sealing arms. A preferred apparatus for starting a lamp having the aforementioned magnetically-responsive arc-initiating structure is also provided which minimizes the size of the electromagnet and isolates the lamp from magnetic fields during operation.

Brief description of the drawing A better understanding of the invention will be obtained by referring to the accompanying drawing, where- 1n:

FIGURE l is a longitudinal sectional view of a highintensity short-arc lamp embodying one form of starting assembly in accordance with the present invention;

FIG. 2 is an enlarged sectional view of the light-generating portion of the lamp shown in FIG. 1 and one form of exterior electromagnet for actuating the starting assembly;

FIGS. 3 and 4 are cross-sectional views along the lines III- III and IV-IV, respectively, of FIG. 2;

FIGS. 5 and 6 are side and front elevational views, respectively, of the pivot pins utilized in the lamp shown in FIGS. 1-4 to provide a freely movable lower anchorage for the starting assembly;

FIG. 7 is a fragmentary longitudinal sectional view of a short-arc lamp embodiment having a modified starting assembly; and,

FIG. 8 is a cross-sectional view of a short-arc lamp of the type shown in the preceding figures and a schematic diagram of a preferred form of actuating electromagnet and associated energizing circuit.

While the present invention can be used with advantage to start various types of gaseous discharge devices which require a higher starting than operating voltage, it is particularly adapted foru's'e in conjunction with high-intensity short-arc lamps designed to be operated in a vertical position from a direct-current power source and it has accordingly been so illustrated and Iwill be so described.

Embodiment I In FIG. 1 there is shown a 1200 watt xenon short-arc lamp 10` having an envelope 12 of suitable light transmitting material, such as quartz, which is terminated by a pair of opposed sealed arms 13 and 14 that hold an enlarged anode 15 and a cathode 16 in spaced apart aligned relationship within the envelope. The anode 15 has a shank 17 which is anchored in a body of quartz 19 that is fused to and hermetically seals the envelope arm 13 in the customary manner. The anode 15 is electrically connected to a terminal cap C by suitable lead-in conductor means such as a number of sealed-in refractory metal ribbons 21 that are attached to the anode shank 17 and to a metal collar 23 that is sealed into the end of the envelope arm 13. The collar, in turn, is fastened to a support rod 25 that is attached to the terminal cap C and anchored in the arm 13.

The cathode 16 comprises a pointed rod that is partly embedded in a fused quartz core 18 that closes the other envelope arm 14 and is connected by a metal sleeve 20 and a second group of sealed-in metal ribbons 24 to the support rod 26 of another terminal cap C. The lamp 10 is designed to operate on a direct-current power source of approximately 40 or 50 volts in a substantially vertical position with the anode disposed above the cathode, as shown in FIGS. 1 and 2. The electrodes are fabricated from tungsten or other suitable refractory metal.

Ignition of the lamp is accomplished in accordance with the present invention by a flexible elongated arcinitiating assembly 30 which, as is shown in FIGS l and 2, is swingably mounted in pendulum-like fashion within the envelope 12 and disposed so that an intermediate portion of the assembly is movable toward and away from the tip of cathode 16 in a lateral direction when the lamp is disposed in its vertical burning position.

The starting assembly 30 is actuated by a magnetic field generated by an exterior electromagnet M (FIG. 2) that is located adjacent the lamp 10 and properly oriented with respect to a magnetically-responsive component that cornprises an integral part of the assembly. In this embodiment, the aforesaid component comprises a flat generally rectangular armature 38 of highly permeable material, such as iron, that is attached to the lower end of the assembly 30 by a laterally extending support or yoke structure 40. This support yoke is located within a cylindrical or tubular portion T of the envelope 12 and is so arranged that the armature 38 faces the envelope wall.

As is shown more particularly in FIG. 2, the upper portion of the starting assembly 30 comprises a thin arcuate strip 32 of suitable resilient refractory metal one end of which is attached to the anode shank 17, as by welding and a few turns 34 of tungsten wire. The lower end of the metal strip 32 is fastened to one end of an angular striker bar 31 of electrically conductive material and to a second refractory metal strip 36 that is attached to the other end of the striker bar and extends downwardly therefrom. The ends of the metal strips 32 and 36 are welded to the striker bar 31 and a few turns 35 and 37 of tungsten wire are desirably wound around each end of the bar as insurance in case of a weld failure. The striker bar 31 is fabricated from a suitable refractory metal such as tungsten.

The lower end of the metal strip 36 is fastened to one end of the laterally extending support yoke 40 which, in turn, is held in such position by a pair of flexible metal support straps 39 and 41 attached to the diametrically opposite ends of the yoke. The lower ends of the straps 39 and 41 are fastened to a collar 42 that encircles a sleeve 22 of vitreous material, such as quartz that encases the shank portion of the cathode 16 and is fused to the quartz core 18.

The armature 38 is thus located on one side of the cathode 16 and the striker bar 31 and the main body portion of the assembly 30 on the other. This permits the pole piece 46 of the electromagnet M to be positioned close to and aligned with the armature 38. Thus, when the magnet M is energized, it attracts the armature 38 and pulls the lower end of the assembly 30 to the left, as viewed and shown in FIG. 2, a sufiicient distance to cause the striker bar 31 to Contact the cathode 16. When the electromagnet M is deenergized, the assembly 30 and striker bar 31 are returned to their original position (indicated by the phantom showing in FIG. 2) by the spring action of the upper metal strip 32 and a metal leaf spring .4 S that is attached to the collar 42 and presses against the upper portion of the quartz sleeve 22. The striker bar 31fis thus movable along a linear horizontal path into make-and-break contact with the cathode 16 by the elec tromagnet M and the restoring force exerted by the aforementioned springs,

Upper hinge assembly In order to keep the size of the electromagnet M within practical limits, the restoring spring system and manner of mounting the starting assembly 30 within the lamp 10 must be such that the assembly can be readily shifted into its make-contact position. An important feature of the present invention is accordingly the manner in which the assembly 30 is swingably attached to the electrode structures. As will be noted in FIG. 2, the arcuate spring strip 32 lis provided with an S-shaped retroverted segment 33 adjacent its upper end that provides a bellowstype hinging action. This not only increases the exibility of -the metal strip 32 but reduces the stress imparted to the metal as it llexes. This latter feature is important insofar as the metal strips 32 and 36 are heated to elevated temperatures during lamp fabrication and when the lamp is operated and thus tend to recrystallize and become brittle. The aforesaid belows type juncture has been found advantageous in preventing the premature failure of the starter assembly due to metal fatigue.

The stress on the opposite end of the metal strip 32 is reduced in a similar fashion by forming a U-shapcd retroverted segment 29 thereat instead of attaching it directly to the proximate end striker bar 31.

Lower rocker-arm assembly The lower end of the starting assembly 30 is swingably held in place by a rocker-arm type anchorage consisting ofthe metal collar 42 which loosely fits around the quartz sleeve 22 and has a pair of pivot pins 44 (see FIG. 4) attached to diametrically opposite sides of the collar by a ring clamp 43. The clamp also overlies the end of the support strap 39 and has a flat portion 50 that accommodates the ends of the spring S and the other strap 41. As will be noted in FIG. 4, the collar 42 is considerably larger in diameter than the quartz sleeve 22 and permits the lower end of the assembly 30 to move a predetermined distance laterally, as indicated by the broken lines.

The lower ends of the pins 44, as shown in FIGS. 1 and 2, engage the tlat upper surface 45 of the quartz core 18 and thus serve as pivot members that support the entire weight of the starter assembly 30. The assembly is accordingly free to pivot on the pins 44 and move laterally a limited distance relative to the sleeve 22.

The frictional forces and drag inhibiting such movement are minimized by providing the pins 44 with fiattened tip portions 51 and smoothly rounded points 52, as shown in FIGS. 5 and 6. The upper shank portions 53 of the pins are desirably flattened to facilitate the sandwiching thereof between the circular collar 42 and retaining ring 43 (see FIG. 4.)

Support yoke assembly Another important feature is the construction of the support yoke 40. As shown in FIG. 3, the yoke consists of a pair of conjoined U-shaped members 48 and 49 that Iprovide a rectangular frame which straddles and is spaced from the quartz sleeve 22 and is thus free to move laterally without touching the sleeve or interfering with the action of the restoring spring S. The members 48 and 49 are held in telescopic relation by suitable locking means, such as friction clamps C, so that the yoke can be collapsed and reduced to approximately half its extended length during the lamp assembly operation. This is an important advantage since it permits the arc-initiating structure 30 and associated components to be attached to the electrode structures and the resulting subassembly inserted as a unit into the envelope 12 through one of its sealing arms. When the subassembly is properly positioned within the envelope, the telescoped support yoke 40 is extended to its full length shown in FIG. 3 and is retained in such condition by the clamps C. The envelope arms 13 and 14 are then sealed to the quartz cores 18 and 19 in the usual manner.

Starting method and apparatus The lamp is started in accordance with the principles of this invention by applying the normal operating voltage across the anode and cathode 16 and then momentarily energizing the electromagnet M. The resulting magnetic iield attracts the armature 38 which pulls the medial portion of the starting assembly 30 toward the discharge path until the striker bar 31 contacts the cathode 16, as shown in FIG. 2. Since the striker bar 31 is electrically connected to the anode 15 by the assembly 30 but is insulated by the vitreous sleeve 22 from the cathode 16, it completes the circuit between the cathode and anode while it is in its make-contact position.

As soon as the electromagnet M is deenergized and the magnetic eld is removed, the assembly 30 is returned to its original position by the restoring spring 32 and S thereby retracting the striker -bar 31 from the cathode 16. The striker bar 31 draws an arc from the cathode 16 and current temporarily flows through the metal spring strip 32 to the anode 15. Gas convection currents generated in the hot atmosphere around the arc simultaneously pump ionized xenon gas into the discharge gap which quickly transfers the arc from the striker bar 31 to the tip of the anode 15. This make-break contact and arcshifting sequence occurs very rapidly and, since the striker bar 31 is automatically cut out of the circuit when in its normal break-contact position, the lamp 10 continues to operate in the normal fashion.

Additional structural features Experience has shown that the arc will not transfer from the striker bar 31 to the anode 15 if the striker bar touches the cathode 16 too far from its tip. The arc will be initiated satisfactorily but the current will continue to ow through the striker bar 31 and spring strip 32 and will not transfer to the anode 15. This diculty is overcome by using an angular shaped striker bar 31 of the type shown in FIGS. l and 2 having a bend or sloped surface the apex of which faces the cathode 16 and is oriented to contact a laterally-protruding part of the cathode. The aforesaid protuberance is conveniently formed by fastening a tungsten washer 28 (as here shown) or a coil of tungsten wire to the cathode 16 ata controlled distance from its tip. The striker bar 31 thus engages a predetermined portion of the cathode 16 near its tip and the latter, due to its small mass, heats up rapidly and minimizes the blackening effect on the envelope during the starting cycle. For optimum results in the case of a 1200 watt xenon lamp of the type here shown, the spacing of the washer 28 from the cathode tip should be approximately 3 mm.

It has also been found that reliable starting will not occur if the striker bar 31 is spaced too close or too far from the cathode 16. The spring portions of the assembly 30 are thus designed to produce a restoring force such that the striker bar, when in its normal break-contact position, is spaced approximately 2 to 4 mm. from the washer 28, and preferably 3 to 4 mm.

Lamp tests have demonstrated that the presence of even relatively weak magnetic elds Within the lamp, once it has been started, cannot be tolerated since they distort the arc and stretch it to such an extent that the lamp extinguishes itself. Thus, the electromagnet M is only energized momentarily to produce a pulse of magnetic power which actuates the starting assembly 30. The magnet is then immediately deenergized. A steady magnetic field from a permanent magnet or a constantly energized electromagnet thus cannot be used to keep the starting assembly 30 in its break-contact position.

Optimum results are also achieved if the magnetic field is configured and oriented in such a way that it produces linear motion of the armature 38 (ie. along a path that is substantially normal to the longitudinal axis of the lamp) with a minimum of rotational torque. To this end the pole piece 46 of the electromagnet M, Ias shown in FIGS. 2 and 3, is at least as large as the armature 38, is disposed parallel thereto and preferably provided with a central longitudinal-extending slot or cavity 47 (FIG. 3) that divides the face of the pole piece into two spaced segments which are substantially aligned with the side edges of the armature.

In view of the foregoing restriction regarding the presence of magnetic fields within the lamp 10 during operation, the armature 38 is fabricated from magnetizable material which will quickly return to a demagnetized condition in the absence of magnetic field. While the armature can be fabricated from soft iron, iron has a Curie point of 770 C. which is too low to permit the lamp to be restarted while it is still hot. (The Curie point is the temperature at which the magnetic properties of a material disappear due to thermal agitation.) Hence, it is advantageous to fabricate the armature from a material which not only is highly permeable but retains its permeability at elevated temperatures. The armature is accordingly preferably fabricated from a material such as Hiperco-27 alloy which contains 27% cobalt `and 73% iron and has a Curie point of 925 C.

While the spring metal strip 32 and leaf spring S may be fabricated from molybdenum, tantalum or tungsten, these metals tend to lose their flexibility at elevated temperatures due to recrystallization or impurity gettering. The aforesaid components are accordingly preferably made from tungsten K metal which has a much higher recrystallization temperature than molybdenum and tungsten and will thus retain its resiliency for a longer period of time under the high temperature conditions which prevail within the lamp when it is operating. Tungsten K metal is an alloy of tungsten and a small percentage (e.g., 2% by weight) of thorium oxide. Since a strip of tungsten (and its alloys) is more rigid than a molybdenum strip of the same dimensions, the aforesaid spring elements if made from tungsten or a tungsten alloy are desirably made of thinner material, or from a pair of superimposed strips which are one-half the thickness of the single strip.

Test data The aforesaid combination of a flexible magneticallyactuable starting assembly 30 and a pulse-energized exterior electromagnet M will rapidly and reliably start a short-arc lamp on the same power supply used to operate the lamp. Starting currents and times obtained on a 1200 Watt short-arc lamp having an arc length of about 5 millimeters, a spacing of about 2.5 millimeters between the cathode tip and striking bar when the latter is in its normal break-contact position, and a lling of xenon at a pressure of 6` atmospheres, and operated on a 65 Volt DC power supply are given in Table I below.

As indicated, higher starting currents provide faster starting. The time required to start a particular lamp will vary since it is dependent upon the spacing between the cathode and the striking bar, the displacement of the initial arc below the cathode tip, the arc length, the gas pressure, the gas purity, the arc current, and the voltage of the power supply and the orientation of the lamp.

Embodment 1I In FIG. 7 there is illustrated another lamp embodiment 10a having the same type of envelope 12a, anode 15a and cathode 16a as in the previously described Embodiment I. However, the protuberance on the cathode tip is omitted and the starting assembly 30a is quite different in that the angular striker `bar 31a is shaped and oriented to span the discharge gap and contact the tips of both the cathode and anode when the stirker bar is in its make-contact position, as illustrated in the drawing. The striker bar thus momentarily short circuits the electrodes during the starting operation when the lamp 10a and electromagnet M are energized.

In addition, the upper spring metal strip `32a is insulated from the anode shank -17a so that the striker bar 31a is insulated from both the cathode and anode when in its break-contact position. The upper metal strip 32a thus does not carry any of the starting current. This is a distinct advantage since the tendency of the strip 32a to gradually recrystallize in use is greatly reduced. This embodiment is accordingly more practical from a life standpoint and is preferred.

The aforementioned insulation from the anode is achieved by attaching the upper end of the strip 32a to a bushing-like structure consisting of a loose fitting sleeve 54 of molybdenum or the like that rides within an annular recess 55 provided in a quartz collar 56 which is rigidly attached to the anode shank 17a by metal tabs 57. The strip 32a passes through a slot 58 provided in the rim of the quartz collar 56 so that the assembly 30a is prevented from rotating. The loose fitting sleeve 54, however, permits the end of the assembly 30a to move a predetermined distance (several millimeters) longitudinally-thus providing a oating suspension that allows the upper spring strip 32a to Hex without being constrained at each end. Actuation of the assembly 30a can thus be effected with a weaker magnetic eld.

The anchorage at the opposite end of the assembly 30a is identical to that of Emlbodiment I and shown in FIGS. 1-4.

Embodment III In FIG. 8 there is shown an alternative form of electromagnet and an associated pulse-energizing circuit for starting a short-arc lamp 10 of the type shown in FIGS. 1, 2 and 7. The pole piece 59 of the electromagnet M is U-shaped and positioned so that its poles are aligned with the side edges of the rectangular armature 3S. The ends of the poles may be curved, as shown, to match the contour of the envelope 12 and reduce the intervening air gap to a minimum. The resulting centralization and concentration of the magnetic field permits the desired linear motion of the support yoke 40 to'be achieved with a very compact magnet.

The solenoid 60 of the ymagnet M is wound around the center of the U-shaped pole piece 59 and connected to one side of a suitable AC or DC power source by a conductor 61. The other side of the circuit is completed by another conductor 62, a variable resistor 63 and a push-button switch 64.

It will tbe apparent from the foregoing that the objects of the invention have been achieved in that an improved starting assembly and apparatus have been provided which will reliably and repeatedly ignite a high-pressure gaseous discharge lamp on the same voltage source utilized to operate the lamp.

While several embodiments have been illustrated and described, it will be understood that various modifications can fbe made without departing from the scope of the invention. For example, the starting assembly can be actuated by a portable permanent magnet that is positioned adjacent the lamp during the starting operation and then removed. The bending stress on the upper spring support 32 can be further alleviated by inserting a movable ele- :ment in the support strap 41 that connects the yoke 40 to the lower support collar 42. This can the accomplished by making the strap in two sections and coupling the sections together so that one slides over the other.

If a soft iron armature is used, it can also be encased in a thin lsheet of -molybdenum (or wrapped with molydenum ribbon) to prevent the possibility of contaminating the 10 lamp with vaporized iron during extended use at elevated temperatures. v

I claim as my invention: 1. A high-pressure electric discharge lamp comprising, in combination;

a light-transmitting envelope containing an ionzable medium and a pair of fixed electrodes that dene a discharge path, separated lead-in conductor means sealed through Said envelope .and connected to the respective electrodes, an elongated arc-initiating structure that is supported by each of its ends within said envelope at a location remote from and along said discharge path and has a exible medial portion that is laterally movable into make-and-break contacting relationship with one of said electrodes, and magnetically-responsive means carried by said structure and adapted, when actuated, to flex the medial portion of said arc-initiating structure and place it in make-contact relationship with said one electrode. 2. The lamp set forth in claim 1 wherein the part of said exible medial portion that makes and breaks contact with said one electrode comprises a refractory metal member that completes an electrical circuit between said electrodes when said member is in make-contact position.

3. The lamp set forth in claim 1 wherein;

the part of said liexible medial portion that makes and breaks contact with said one electrode comprises a refractory metal member which, when in make-contact relationship with said one electrode, is spaced from the other of said electrodes, and

said member is connected to said other electrode by a flexible conductor.

4. The lamp set forth in claim 3 wherein said refractory metal member has a protruding portion that faces toward said one electrode and is so oriented that it engages a part of said one electrode that is spaced a predetermined distance from its tip.

5. The lamp set forth in claim 3 wherein said iiexible conductor comprises an integral part of said elongated arc-initiating structure.

6. The lamp set forth in claim 2 wherein;

said refractory metal member is so dimensioned and oriented that, when in make-contact relationship with said one electrode, it spans the discharge path and 5 also contacts the other electrode, and

said refractory metal member when in its break-contact position is electrically isolated from both of said electrodes. 7. The lamp set forth in claim 1 wherein said magnetically-responsive means comprises a magnetizable member that is attached to the flexible unsupported medial portion of said arc-initiating structure.

8. The lamp set forth in claim 1 wherein; said elongated arc-initiating structure is so supported that the flexible medial portion thereof laterally moves toward and away from said one electrode along a linear path, and said magnetically responsive means comprises a magnetizable member that is disposed adjacent a wall of 70 said envelope and is supported in such position by a laterally extending yoke that is attached to the flexible medial portion of said structure. 9. The lamp set forth in claim 1 wherein; said lamp has a longitudinal axis and is adapted to be operated on a directcurrent power source,

said electrodes comprise a cathode and an anode,

said lamp is further adapted to be operated in a position such that the anode is disposed above the cathode,

said elongated arc-initiating structure comprises a flexible assembly of conjoined refractory metal strips 10 portion that is spaced a predetermined distance axially from said tip, said striker bar is of angular configuration and disposed so that its apex contacts the laterally-protruding portion of said cathode, and

that is suspended in longitudinal pendulum-like the end of said refractory metal assembly that is fastened Vfashion within the envelope in a position such that to said anode has a retroverted segment that provides its medial portion is swinga'ble toward and away from a bellows-like hinge action. the discharge path in a lateral direction, 16. The lamp set forth in claim 9 wherein: the electrode-contactor portion of said flexible assem- 10 said lamp comprises a short-arc lamp,

bly comprises a striker bar of refractory metal that one end of said flexible assembly is hingedly attached is fastened to the swingable medial portion of said to and is insulated from said cathode, assembly and is oriented to contact the cathode, and the opposite end of said assembly is coupled to and insaid magnetically-responsive means comprises a body sulated from the anode by a bushing-like structure of magnetically permeable material that returns to that allows the said end of the assembly to move a substantially demagnetized condition in the absence limited distance axially but prevents it -from rotating, of a magnetic field. and 10. The lamp set forth in claim 9 wherein one of said said striker bar is of angular configuration and so diconjoined metal strips constitutes a spring that maintains mensioned and oriented that it bridges the gap bethe striker bar in break-contact position in the absence of 20 tween said electrodes and contacts both of them a magnetic iield. when in the make-contact position.

11. The lamp set forth in claim 9 wherein; 17. Apparatus for starting an electric discharge lamp said flexible assembly is swingably supported at each that requires a higher starting than operating voltage has end, and an envelope that contains a pair of fixed electrodes, which said body of permeable material is located proximate a 2 apparatus comprises:

CII

wall of said envelope and is supported in such position by a horizontally extending yoke that is attached to a medial part of said assembly and straddles and is spaced from the cathode.

an armature of magnetizable material carried Vby an elongated arc-initiating structure that is hingedly mounted within said envelope and has a flexible electrically-conductive medial portion which is adapted 12. The lamp set forth in claim 9 wherein: 30 to make and break contact with one of said electhe portion of said envelope that contains said body of trodes when said structure is actuated, said armature permeable material is of tubular configuration, and being secured to said flexible medial portion at a Said body of permeable material has a substantially location adjacent the wall of said envelope,

planar face that is disposed toward a wall of -the y an exterior electromagnet disposed adjacent said lamp tubular portion of said envelope. and oriented so that the pole piece of the magnet is 13. The lamp set forth in claim 9 wherein; located directly opposite said armature, said lamp comprises a short-arc lamp, the pole piece of said electromagnet being of such size said envelope is terminated at each end by opposed seal and conguration that the side edges thereof are Subarms in which the cathode and anode are respectively stantially aligned with the side edges of said armature,

anchored,

the portion of said cathode adjacent the arm in which it is anchored is encased in a vitreous sleeve,

one end of said flexible refractory metal assembly is hingedly fastened to said vitreous sleeve and is thus insulated from said cathode, and

the opposite end of said assembly is hingedly fastened to a part of said anode remote from the arc-sustaining tip thereof and is thus electrically connected to said anode.

14. The short-arc lamp set forth in claim 13 wherein;

the end of said flexible metal assembly is fastened to said vitreous sleeve by a loose-fitting collar,

the inner end of the seal arm proximate said collar defines a substantially fiat laterally-ex-tending surface, and

a pair of spaced pins depend from said collar and contact said surface thereby permitting the attached end of said flexible assembly to pivot and also move laterally a predetermined distance with a minimum of friction.

15. The short-arc lamp set forth in claim 13 wherein;

said cathode has a pointed tip and a laterally-protruding circuit means for applying an operating voltage across said electrodes, and

means `for momentarily energizing said electromagnet and thereby producing a magnetic field that attracts said armature and pulls the flexible medial portion of said arc-initiating structure along a linear path such that it makes and then breaks contact with said one electrode While said electrodes are energized.

18. The apparatus set forth in claim 17 wherein;

said armature is of planar configuration and composed of material which is highly permeable,

the pole piece of said electromagnet comprises two spaced pole segments that are substantially aligned with the side edges of said armature, and

the portions of said pole segments that face the lamp envelope are curved to match the contour thereof.

References Cited UNITED STATES PATENTS 2,128,861 8/1938 Tonks 313-170 X JAMES W. LAWRENCE, Primary Examiner. R. F. HOSSFELD, Assistant Examiner. 

